This invention relates generally to an electrothermal reactor to provide controlled decomposition of chemical compounds and mixes such as hydrazine, hydrazine blends and monomethyl hydrazine with minimal use of hot and/or catalytic surfaces.
The use of hydrazine type fuels as a source of energy has been known for quite sometime. When hydrazine liquid is caused to react, it molecularly dissociates forming hydrogen, nitrogen and ammonia with intermediate combinations accompanied by the exothermic release of a great deal of energy. Dissociation of hydrazine blends produce related reaction products and exothermic energy release. As the hydrazine will generate a large quantity of hot gas, numerous areas of applications have been derived for such fuel uses. As an example, the military arsenal includes a number of munitions incorporating hydrazine assisted power supplies, propulsion systems on some rockets and spacecraft, auxiliary source of power to maintain hydraulic pressure in aircraft, to name just a few of the areas of use.
Reactors presently employed for such technical applications as rocket thrusters and gas generators require extensive, expensive and difficult to refurbish catalytic surfaces to initiate and stabilize the reaction. Due to causes such as thermal shocks, thermal cycles, contaminating flow, the catalyst "beds" tend to mechanically/structurally deteriorate and/or become "poisoned" (loss of catalytic reactivity) thereby losing effectiveness. Further, operation of a catalyst bed reactor with most hydrazine blends is limited to single firings due to bed poisoning. In addition, the catalyst type reactor is not particularly efficient when used for pulsed or low flow rate operation.
Two other methods used to cause the hydrazine to react are: to have pyrotechnic energy release or to introduce a preheated gas flow into the reaction chamber. Heat from external source, i.e., chemical, pyrotechnic and/or electrical, raises the temperature of the reactor or a portion of the reactor such that the injected fluid such as hydrazine will vaporize and thermally decompose. Typically, a temperature of 400.degree.-500.degree.F. is needed to cause hydrazine to react. Once started, the reaction may be self-sustaining and the external heating may be terminated.
Direct electrical heating of the reactor will also provide sufficient temperature and energy for decomposition. Two previous attempts to provide reactors of the direct electrical heating type had significant limitations. In one, an exposed electrical filament was used to generate the heat. This filament was susceptible to degradation. The reactors were unable to operate for more than several minutes steady state without performance degrading heat sinking because of the temperature limitations of the electrical heater insulators. In this type reactor, the insulator constituted a portion of the reactor chamber wall. In addition, to insure insulator-structural integrity, the operating temperature was reduced by heat sinking (conduction of heat away from) the reactor to its support. The other uses a standard external filament (i.e., Nichrome heater element) and an internal semi-catalytic screen pack (typically platinum). Reactors featuring such screen packs have some of the disadvantages listed for the catalytic reactors.
The state-of-the-art of present hydrazine type reactors generally features small orifice injection of the liquid hydrazine for atomization or small droplet formation. The hydrazine liquid is injected through small ports or apertures having screens thereacross such that the liquid passing through the port or screen would essentially be atomized or broken up into small droplets. The small ports or screen have a life-limiting effect on the reactor since the small ports or screens will undergo degradation, sufficient at times to reduce and/or restrict input flow.
Accordingly, it is an object of this invention to provide an electrothermal reactor which will reduce or eliminate the aforelisted problems.
A further object of this invention is to provide an electrothermal reactor in which small port or screen atomization injection methods have been eliminated while still permitting effective atomization of the liquid.
And yet another object of this invention is to provide an electrothermal reactor in which the heating element is formed with an external metal cover over an insulator which encapsulates the filament heater.
A still further object of this invention is to provide an electrothermal reactor in which the fuel is injected into the reactor as a liquid wherein vaporization takes place within the reactor.
And yet a still further object of this invention is to provide an electrothermal reactor which uses atomizing injectors wherein the fuel is injected into the reaction chamber as a vapor.